Fuel pumping and pressurising plungers of Electronic Unit Injectors (EUI), Unit Injectors (UI) and Electronic Unit Pumps (EUP), are operated in a reciprocating manner. In a known driveshaft arrangement or assembly 1, as illustrated in FIGS. 1a and 1b, reciprocating motion of a plunger 90, as indicated by arrow P, is caused by a rotating cam 2 located on a shaft 12. The cam 2 is formed of a base cylinder section 8, and an integral further section 10, protruding from part of the circumference of the base cylinder section 8. The cam 2 therefore has an outer surface 4 defined partly by the outer surface 4a of the base cylinder 8, and partly by the outer surface 4b of the further section 10.
The cam 2 operates on a plunger 90, either directly (as illustrated in the FIGS. 1a and 1b), or indirectly via a pivoting rocker arm (not shown). Lift is transferred to the plunger 90 or rocker arm in the direction of arrow L, via a lift point 6 on the outer surface 4 of the cam 2, where the outer surface 4 of the cam contacts with the plunger 90 (or rocker arm). In the orientation of FIGS. 1a and 1b, point 6 is the uppermost point of the outer surface 4 cam 2.
The cam 2 rotates about a centre of rotation, defined by a longitudinal central axis 14 of the shaft 12, which is coincident with a central axis 70 of the base cylinder section 8. As the cam 2 rotates with the shaft 12, the contact point between the cam 2 and the plunger 90, moves around the outer surface 4 of the cam, i.e. lift point 6 moves relatively around the outer surface 4 of the cam 2.
As illustrated in FIGS. 1a and 1b, the instantaneous lift L of the cam 2 is calculated as below:L=A−B; where A is the distance from a central axis 14 of the shaft 12 to the lift point 6, and B is the distance from the central axis 14 of the shaft 12 to the external surface 4a of the base cylinder section 8, i.e. a radius of the base cylinder section 8.
During part of the rotation cycle, when the lift point 6 occurs on the external surface 4b of the further section 10, the distance A will vary in accordance with the external profile 4b of the further section 10. During the part of the rotation cycle when the lift point 6 occurs on the external surface 4a of the base cylinder section 8, distance A will be constant and will be equal to distance B.
FIG. 1a illustrates a rotational position of the cam 2 which provides maximum lift, Lmax, i.e. lift point 6 is at a maximum distance from the centre 14 of the shaft 12, and distance A is therefore maximised.
FIG. 1b illustrates a rotational position of the cam 2 providing minimum lift, i.e. lift point 6 is at a minimum distance from the centre 14 of the shaft 12, and distance A is therefore minimised. In this position, A and B are equal, therefore the minimum lift Lmin is zero.
Typically, the prior art embodiment of FIGS. 1a and 1b also provides a constant plunger rate period. A known disadvantage of the prior art embodiment such as that illustrated in FIGS. 1a and 1b is that the maximum lift Lmax of the driveshaft assembly 1, and therefore the travel of the plunger 90, is predetermined and fixed, as each driveshaft assembly has a set value of B and set maximum value of A. To obtain a different value for the travel of the plunger 90, it is necessary to disassemble the driveshaft assembly 1 by removing the cam 2 from the shaft 12, and replacing it with an alternative cam having a different external profile, i.e. a different value of B and/or maximum A, and/or by replacing the rocker arm or changing the pivot point of the rocker arm.
Accordingly, in prior art embodiments, it is difficult to accommodate the differing plunger travel requirements. For example, it is difficult to accommodate the specific lift range requirements of different EUI, UI and EUP families, which could typically range from 9 mm to 19 mm.